A new crosslink has been isolated from cow skin. This crosslink derived from lysine, hydroxylysine and histidine is stable to acid hydrolysis without a prior chemical reduction. It may be a naturally reduced crosslink. Further investigations as to the process in which such "naturally reduced" crosslinks are produced is projected. Newer methods for crosslink analysis employing flourine NMR (a fluorine containing carbonyl reagent) are in progress. Several fluorine containing carbonyl reagents have been synthesized. Elastins from various sources have been examined in regard to thier crosslink maturation profiles and in these studies milder methods of elastin isolation have been employed. There are reproducible differences in maturation profiles with elastins derived from different tissues. Further studies are in progress to quantitate these differences and to apply these techniques to the examination of pathological tissues. Further characterizations of the new bone protein, osteocalcin, are underway and recent work indicates that a role for Vitamin K in post-translational carboxylation appear likely. BIBLIOGRAPHIC REFERENCES: Gallop, P.M. and Paz, M.A. Post-translational protein modifications, with special attention to collagen and elastin. Physiol. Revs. 55: 418-487 (1975).Hauschka, P., Lian, J. and Gallop, P.M. Direct identification of the calcium-binding amino acid, gamma-carboxyglutamate, in mineralized tissue. Proc. Nat. Acad. Sci. U.S.A. 72:3925-3929 (1975).